Pulse regenerator



Nov. l0, 1953 R. L. CARBREY ET AL PULSE REGENERATOR 4 SheetsSheet l Filed July 27. 1950 ATTORNEY Nov. l0, 1953 R. L. CARBREY ET Al. 2,658,997

PULSE REGENERATOR Filed July 27, 195o 4 sheets-sheet 2 NOV v10, 1953 R. 1 CARBREY ET Al.

PULSE REGENERATOR 4 Sheets-Sheet 3 Filed July 27. 1950 R. LgcARa/PEY /NvE/vons: c. c. cur/.ER

El PI :wvl-ICA I o m Q u m m. .um

C. B. H. FELDMAN Arron/VU Nov. 10, 1953 R. l.. CARBREY ET AL 2,658,997`

PULSE REGENERATOR 4 Sheets-Sheet 4 Filed July 27. 1950 .4 .5 RELATIVE VOLTS INPUT R. L. CARBREY C. C. CUTLR C. B. H. FELDMAN ATTORNEY Patented Nov. 10, 1953 UNITED STATES PATENT Fl'-lC`l?.vv

PLSEREGENERATOR Robert- L. Carni-ey; Summit, Cassius-C. Cutler,

Gillette, and CarlB. H. Feldman,- Summit, N t 3., assignors to' Bell'L Telephone Laboratories', In;- yoorporateiLNew York, N. Y., a oorp'oration'o'l'` New York.

Application July 27,-1/950, Serialo 176,233"

(Cl. Z50- 27) 12`V Claims. 1 This invention relates to signal regeneration and more particularly to circuits for the regenerationof microwavepulses which comprise circulating pulse regenerators. Circulating pulse generators similar to the circulating pulse` regenerators herein referred to are described in a copending application of C. C. Cutler, Serial No. 118,889, dated Sepetember 30, 1949, Patent No. 2,617,930, dated November 1l, 1952. V

rIt isan object of this invention to regenerate microwave pulses.

It lis also anobject of the inventionto determinefrom a microwave. signal modulated with recurrentV pulses and. spaces which ofthe signals` are more likely to have been originated as pulses and which Were morev likely to have been originated as spaces. Further, it is an object to increase those signals which are determined to be pulses to a uniform amplitude and to reduce allV othersto zero. It is alsoan object of the invention to retime the signal pulses.

Another object of the invention is toV gate a.

short representative segment of an incoming signal at the mid-period of each nominal pulse occurrence time into a regenerative repeater and then to gate the segment into an output circuit after having beenallowed to circulatethrough the pulse regenerator for a predeterminednumber of times.

A circulating pulse regenerator is a loop circuitv Which,- inone embodiment, comprises an expand-y er, a limiter, an amplifier, alter and' a delay circuit. Pulses circulating in the loop Willlbe sharpened by the expander which increases the amplitude of` high level signals relative to. low levelsand will be limited atapeak amplitude established by'the limiter. The amplifier iS adjusted toV give the loop unity gain at a norminal pulse amplitude so that pulses of that amplitude will tend to circulate indefinitely unless removed from the loop. The delay circuit controlsthe` with a uniform amplitude since it is necessary at a receiver to detect' only the presence or absence of a pulse during a particular interval of` time. Due'to noise'and other interference, however, the pulses may become varied in amplitude and the spaces may be replaced by an appreciable signal.

Vnoisedisturbanc@sin:transmission to the"succeed'-` repeater W-thutllfetaiilngfthedistlllfbahes acquired in the preceding transmission path.

A pulse; repeater inaccorda-nce with specific: embodiment of the .invention .takes a' very short sample of theV incoming signahproportional.. its amplitude at the: midi-periods:` of. the; nominal pulse occurrence time; vIf the signal from; whichl thefsample is takenv originated as 'a puise, it. is'- probablethat, atv the repeater,Y it will beimorei than one-.half of its original sta'.'ndarclamplitude;Y Conversely, if itl originatedasa space, .itis-equally probable that the samplewill loe-less thanone half of a; standardpulse amplitude. This. of course assumes that the chosen standard lampli-- tude is sufficient to give a minimum signal to noise ratio of. six decibelsA forI most transmissionr conditions.y The repeater is therefore designed.. atamplify all samplesk of greater than'the. half-Y standard amplitude and attenuate all others.4 The elements .which perform these operationswill. usually not increase the pulsesto standardamplitude orv attenuate thev noisey to zeroY iny onev operation onthe sample.l Therefore, the. sam ples are subjected toy thev reshapingY operation. more than once by circulating them through the pulse regenerator .for asuicentnumlo'er of timesA to performthe requiredreshaping. limiter isz included .in the regeneratoricircuitto standardizethe amplitude ofthe reshaped pulses. Timing circuits areprovicled to introuce the samples into the circulating regenerator and to abstract the reshaped pulses after their predeterminednumber of trips through the loop.

The .invention may be better understood by a consideration ofthe following detailed description of illustrative embodiments v/henreadlin' aocordance with Athe attached drawings inwliichf Fig. 1 is a block schematic diagram of` a pulse repeater embodying principles ofthe invention:

Fig. yZisl a schematic diagramof a specific. re1- peater ofthe ytype shown in Fig. '1;'

Fig. 3 comprises Wave forms illustrative' offV Fig. 2;

Fig. i is aplctorial view' of ahybridjunction;

Fig. 5 shows typical characteristic curvesofl'an expander, and a limiter. both individually and, combined;.and

Fig. shows, in schematic, a hybrid gate.

The. general operation of a specific repeater illustrative of the present invention will' now be described with particular reference to Fig. 1. The incoming signal comprising pulses and spaces is received by the antenna II and passes into the hybird junction I2. Although the signal was originated with pulses of a uniform amplitude, the signal when received at the repeater may be distorted by noise, for example, and appear as illustrated by waveform I of Fig. 3. Half of the power entering the hybrid junction I2 is applied to a timing circuit which comprises the rectifier I3, a pulse rate filter I4, an amplifier I5 and a control pulse generator I6. The lter I4 is a narrow band pass lter tuned to the nominal pulse repetition rate of the incoming signal and its output will be a sine wave whose frequency is accurately determined to be the average repetition frequency of the input pulses. Three pulse trains are derived from the amplied since wave by the pulse generator IE for uses which will subsequently be apparent.

The power entering hybrid junction I2 Iwhich is not applied to the timing circuit is applied .to the input of gated 4amplifier I'I. The gate I is normally closed but is opened for a relatively small portion of a pulse period at the mid-period of the-nominal pulse occurrence time by the control wave appearing on lead I8 which is the first of the aforementioned three pulse trains. (A pulse period is herein defined as the nominal time between adjacent pulse centers.) A narrow segment of the incoming signal is thus gated and amplified by amplifier I'I atl each pulse occurrence time. The gated segment is applied to the input of hybrid junction `I9 which comprises the input to the circulating pulse regenerator.

The circulating pulse regenerator is a loop circuit which comprises the expander 2I, limiter 22, ampliiier 23, ilter 24, and delay circuit 25. The order in which the elements of the loop circuit are connected together may be varied and, as shown, is illustrative only. Further, the desiredcharacteristics of the loop may be embodied in a lesser or a greater number of devices than that shown. As previously mentioned the eX- pander will amplify all pulses greater than a predetermined amplitude and attenuate all others. The limiter 22 determines the peak amplitude to which the circulating pulses can be increased and the amplifier 23 has sufficient gain to make up the losses of the loop so that it has unity gain for pulses of one-half standard amplitude. The fil-Y ter 24 is a broad band device denoting the selectivity of the entire loop circuit. The delay circuit 25 controls the period of the circulating pulses and hence controls the time that a pulse will return to the point of its injection into the loop, viz., the hybrid junction IB.

Amplifier 23 is a gated device which is open while the pulses are circulating for their predetermined number of trips through the loop. Amplifier 26 is connected to the output of the loop which comprises the hybrid junction 21 and is also a gated device but is normally closed. Under the control of the pulse train appearing on output' lead 28 of generator IB, the amplier 26 is gated open when a pulse segment h-as completed its' predetermined number of trips through the expander 2I, and amplifier 23 and appears in hybrid junction 21 so that the reshaped segment is amplied and gated into the output. The pulse is shaped by filter 29 and, after amplifica.- tion by amplifier 30, is transmitted by the antenna 3l. After a pulse segment has 'been gated out of the loop, the control pulse train ap- Fig. 3, enters the p-arm of hybrid junction I2.

pearing on lead 32 closes the gated amplier 23 the next occurrence time of the now unwanted pulse at the input of amplifier 23 to insure complete removal from the loop.

As previously mentioned, the pulse segments are recirculated through the reshaping portions of the loop circuit, viz., the expander, limiter and amplifier 23, to insure that the pulses are increased to the standard amplitude determined by the limiter 22 and to attenuate the noise to zero. If the total delay of the loop is less than one pulse period it is theoretically possible to recirculate a pulse through the expander, limiter and amplifier without the intervention of a subsequent pulse. Y For example, if the total loop delay is equal to one-tenth of a .pulse period and if the sample taken from the incoming pulse is equal to or shorter than one-tenth of a pulse period, a pulse segment may make ten trips through the loop without interfering with a subsequent pulse.

At microwave frequencies, it may be impossible to attain such short delays in which case it may be advisable to adjust the loop delay by means of the delay circuit 25 to make it greater than a pulse period, for example 1.1 periods. Ten trips through the loop without interference would still be possible although the pulses will be interleaved as will be illustrated hereinafter. ments from ten different pulses may be circulating through the loop during any one pulse period.

Other loop delays are also possible. The major consideration is that a pulse during its predetermined circulating period must not return to the loop input at the occurrence time of a subsequent pulse.

ments will be sufficiently short so that they can be recirculated through the loop as many times as desired Without interference.

The invention will now be described in detail with reference to the specic embodiment shown in Fig. 2 and to the wave forms of Fig. 3. In the present illustration, the loop delay is 1.1 pulse periods and the length of the segments is .1 of a period. Input signal energy from the antenna II of Fig. 1, illustrated by wave form I of hybrid junction is illustrated pictorially in Fig. 4 and is described in Patent 2,445,895 to W. A. Tyrrel, dated July 27, 1948.

The hybrid junction illustrated in Fig. 4 comprises two pairs of conjugately related wave guide arms. One pair comprises two colinear arms designated o: and b, respectively'. The other pair comprises an arm joined in the electrical plane of the colinear armsl and another joined in the magnetic plane of the colinear arms. Since electromagnetic energy which enters the arm joined in the electrical plane Will be in phase in the a and b arms at equal distances from the junction, the arm is identified as the parallel or p-arm. Similarly, from the phase relations of energy entertionship of the arms there is no direct coupling That is, seg-4 Further, the maximum number of trips through the loop consistent with good opbetweenlthe .1n-ands. armszor` betweenthesa'fand b'arms. Thehybrid junction I2 asused herein makes noespecial use of theconjugacy feature but-.isuemployed merely-y as convenient tapping means.

The energy which entersl the p1 armv ofe the hybrid Y junction I 2 will therefore divide between the aand harms. The` s armlisterminatediin its characteristic impedance to absorb Vany 'energy which may be-reected'froml either theaI or b arms'. Energy enteringV` the b' arm is` rectified bythe'fcrystal'rectier I3 and* applied tofthefilter I4f Which,- as previously described; isIarnarlrowl bandflter tuned -to the nominalpulse-repe' tition rate. 'I'hesinusoidallyrvarying output. of filterl4 islamplied by amplifier I5 and applied to' the control pulse generator I6'. The control pulse wave forms generated by generator I 6 -are illustrated as'wave forms II, V, and VIliof 'Fig.`3' and may be generated by any-of Vthe meansfvvell known in the art such as clipping, delay line pulse shortening or delay line time positioning. These three wave forms appear on outputv leads I8; 32, and 28 respectively.

Energy entering the a, arm of hybridjunction I2.is applied to the input of traveling-'Wave amplifier IY'I illustrated schematically vas comprising avcathode 4I,- control-grid 42, accelerating anode 43; helix 44 and collector 45. Traveling-wave ampliersare described inarticles inthe Febru ary 1947 Proc. Il R. E. entitled Traveling-Wave Tubes byJ. R'. Pierce and L. M. Field at page 108, Theory of-the Beam-Type vTraveling-Wave Tube by -J-. R; Pierce at page 111 and The'Traveling-Wave Tube, as an Amplifier at Microwaves by R. Kompfner at page'124.

Appropriate bias potentials are applied to the electrodesy ofthe traveling-Wave amplifier I'I by the battery 46. The grid 42 is connectedthrough the resistor 41 `to a pointon `the battery46 suili'- ciently'negative with respect to the cathode to cut 01T the ow of electronsfrom-the cathode.- Thetube thereforewill not amplify and is hencenormally inoperative -or' closed. Somel energy will pass lthrough the tubeirrespectiveof the cut-ofi beam but with a normal tube` thisenergy-will be over thirty decibelsdown 'from' the -amplified output and hence negligible.

The' gate I1 is opened at the mideperodof' the nominal pulse occurrence" time by the^ positive control pulseswhichfappear Yon output lead I8 ofA the pulse generator I6. Whena positive control pulse is applied` tothe" control grid 42 through' condenser 48, the grid is driven` tov the cathodepotential and thetube IT will' amplify for the duration of the control pulse. For illustrativef purposes; these control pulses" are illustrated inwaveform II of' Fig. Stand' are' oneitenth of a pulse period in length; Therefore; a* short segmentf'of thefinputrsignal, proportional toits instantaneousV amplitude isgated through'Y and'amplied for one-tenth ofth'e periodfollowedf by a blank interval of"nine-tenthsof'aA period. The resultingx envelope` of the" energy' appearing Wave' 'guide' 49vv will' appear" as--wave Expander@ I comprises'f af hybrid? junction.ofithetypeashown' inlFig; 4, buthwithf thisl valueif previously greater.y

pulse.` of' exactly one-half standard amplitude 6. the :conjugatefasand b? arms=terminatedfin1crysta1 rectifiersw56'; The crystals 50.-.' provide f afzvariable impedance termination: for-the .wave :guide: secetions andicontrol the amounti of-fenergy thatzis: reflected? from the az. and; bf arms... One'.` of the arms, for example: the: b arm 1 is 'a a a. quarter.: otra Wavelength longer than theother;

sorthatzthe. azand brarms reflect energy; into'. the s farm. ink an 'additiveT manner.

The expander'characteristic shown as .curve a ofFg. zisobtained byv matching thesimpedance of.'v the' crystals tothe.- impedance of their-"cori-l respondirlgaarms for: low signal amplitudes'.` This results in substantially'no reection ofthe low levels.`A fromV the; ar and. b, arms. and hence; rela@` tively high attenuation .of suchl signals. As `theinfput :signal 1eve1 increases, the. a andzby armswill become progressively mismatcheddueto the non-L ohmic: resistance characteristic of 'crystal `rectiers ,and the `higherlevel will. be 4more completely reected. Thelevel at Whichthe crystals3arek matched. tov their respective wave guide sections iszcontrolled` by vimpedance' matching devices; in a .welleknown manner;v An expander: of theftype described isidisclosed inta copendingrrapplication oisCl` C.: Cutler',` Serial..No. 118,890, IiledxSepteme berBO, 19,49..

The expanded output-from= thesiarm 01E-the expander is'.` applied .torthe input? of the: limiter 22zwhiclr Vis. structurally 1 similar-` to thek expander 21.` However, the crystalrectifiers v5.1 ofthelim.-` iter are matched toztheir" respectivearmsatia predetermined highlevel. torlimit the .amplitude ofethe pulse segments tor thev desiredipeakamplitude. The 1 limiterv characteristic isshown as curve. b'of Fig. 5. A limiterof the. typedesorihed is-.zdisclosed in `acopending applicationof A.. F.' Dietrich, Serial No.y 118,856, led September 3.0,` 1949. Thevnet effect of thefexpanderand limiter isI illustrated bythe combined.. expander-limiter characteristic; shown as curve cof Fig. 5.`

As' previously mentioned', it'fis` desired to reduce all Si pulsefsegments: oi' less than oneehalf( Ofi a: standard` amplitude tozero so thatA a space wrlI resulti and toi increase allV pulse: segments" oi" greater than one-half standard amplitude to unity standard amplitude, or, to limit them tol Therefore;l a

should remain" unchanged by the loopv andshence'. controlsl the loop again.V

'Idestablis'h7 unity loop `gain for pulses ofi-oneshalfstand'ard amplitude; the` pulse segmentsare.

amplified' by traveling-wave amplier- 23 which compensates for the losses distributed through the loop: Ampli'er 23 islsimilarto ampliier I'I with the biasing potentials supplied by battery 52. Also, control pulsesfromgenerator I6f`are applied by theA lead 32 and condenser 53 to the control grid of the tube. It may be seen by reference to wave formv V of Fig. 5' that the control pulses supplied. over lead 32. are positive while the. pulse segments are circulating in their predetermined manner so that the amplier 23` is a normally open gate..

The curves of Fig. 5 have been plotted with a double ordinate. The right-hand ordinate in dicates'therelatve output of only the expander andor limiter. The left-hand ordinate indicates the output of the complete loopy and in-l cludesthe amplification introducedv by ampli-r er 23 as well as the distributed lossesfinithe loop. It'may be seen that the unity loop gain line intersects the combined expander-limiter characteristic at one-half standard amplitude relative input so that a pulse of this amplitude will theoretically circulate unchanged. In a practical case, small variations will change such a pulse sufficiently to cause it to go one way or the other.

From the characteristic of the complete loop, it may be seen that loop gain is reduced below unity as the signal level decreases below one-half standard amplitude. For pulses of greater than one-half standard amplitude, the loop has a gain of greater than unity as long as the pulses do not exceed the limit set by the limiterV 22. For the chracteristic shown, the loop gain increases as the input level approaches .7 unit of standard amplitude at which level the limiter prevents any appreciable further increases. Inputs of greater than .'1 unit reappear at the expander 2l inputr with standard amplitude.

The amplified and partially reshaped pulses appearing in wave guide 54 are returned to the input of expander 2| by way of the p and a. arms of hybrid junction 21, the iilter 24 comprising the irises 55 the coaxial line 25' and the a and s arms of hybrid junction i9. The total delay of thel loop is controlled by cutting the coaxial line 25' to the proper length which in the present illustrative case would be sufficient to give the loop a total delay of 1.1 pulse periods.

Part of the power applied to hybrid junction 21 is applied to the input of traveling-Wave amplifier 26 which is similar to amplifiers i1 and 23, and is biased in a similar manner by battery 56. When a pulse which has not completed its predetermined number of useful trips through the loop appears in hybrid junction`21, the electron beam of tube 26 is cut on by the negative bias on the -grid and no appreciable energy appears in output Vwave guide 51. However, when a pulse which has made six trips through the expander 2 I, limiter 22 and amplier 23 appears in hybrid junction 21, a positive pulse from control pulse generator I6 is applied to the control grid of tube 26 by Way of lead28 and condenser 58. The reshaped pulse will therefore appear in ampliiied form in wave guide 51 and after snap--V ing by filter 29 will be passed to the amplier 30 and output antenna 3B of Fig. l.

Even though a pulse is gated out of the loop, a portion of it will continue to circulate in the loop and if not removed would eventually interfere with a subsequent pulse. To this end, a negative pulse is applied to the control grid of amplifier 23 from generator i6 at a time after the pulse is gated out of the loop by amplifier 2.6 equal to the delay of the loop between the hybrid junction 21 and the input to amplifier 23 by Way of the coaxial line section 25. The pulse segment therefore completes seven trips through the expander and limiter but is blanked on the seventh trip by amplifier 23.

The timing and reshaping of the pulse segments will now be explained with particular reference to Fig. 3. A sample of the input wave, wave form I is taken at the mid-period of the nominal pulse occurrence time by theaction of control pulses, wave form II which open the input gate. The gate segments appearing in the output of the input amplifier wave form III are proportional in amplitude to the instantaneous amplitude of the signal wave and equal in length to the length of the control pulses which open the gate.

' The pulses appearing in hybrid junction I9 are shown as wave form IV. The first gated pulse segment, pulse A, is just greater than the slicing level which is the half standard amplitude previously referred to. Assuming that its actual magnitude is .51 units, it may be seen from the loop characteristic of Fig. 5 that after one trip through the expander, limiter and amplifier, pulse A will reappear after a delay of 1.1 pulse periods at the input of the expander as a loop of .52 unit. This pulse is indicated on wave form IV as pulse Ai, the subscript denoting the number of completed trips through the loop. A second trip will increase the pulse to .545 unit, as indicated at A2 and a third trip Will increase the segment to .62 unit as shown by As. The fourth trip will increase the pulse to .83 unit and a fifth trip will bring it to the standard amplitude of one unit as shown at A4 and A5 respectively. The pulse Will therefore remain unchanged by its sixth and final trip through the loop.

Pulse segment B is less than .5 unit and is attenuated to zero on the second trip through the expander. Pulse C has an amplitude of .49 unit and is not removed until after the fourth trip through the loop. Pulse D is exactly unity amplitude and circulates unchanged. Pulse F is greater than unity amplitude and after being limited to one unit on its first trip through the loop, circulates as a pulse of standard amplitude.

The envelope of the pulses appearing at hybrid junction 2 are shown as wave form VI of Fig. 5. rIhese pulses have not been delayed by delay line 25 but only by amplier 23 and associated wave guide which fact is indicated by the prime imposed on the pulse designations. The timing of the control pulses of Wave form VII is determinted from the delay between hybrid junction I9 and hybrid junction 21 and the relative location in a pulse period of a pulse segment which has completed its predetermined number of useful trips through the loop. In the illustrative example, the delay between hybrid junctions IS and 2i is .25 pulse period. Further since the loop delay is equal to 1.1 periods and each pulse makes six reshaping trips through the expander and associated amplifier, a pulse segment is gated from the loop on the trip which it commences centered at .5 unit of a pulse period that is, 5.5 periods after having entered hybrid junction i9. The control pulses of Wave form VII which open the output gate are therefore delayed .5 plus .25 unit of a pulse period with respect to the control pulses of wave form I which open the input gate. This may readily be seen from the Wave forms of Fig. 3.

The output pulses after amplication by amplifier 26 and shaping by filter 29 appear as shown in wave form VIII.

As previously mentioned, the portion of a pulse which remains in the loop after its speciiied reshaping trips through the loop must be removed or it will continue to circulate and eventually coincide with a subsequent pulse, namely, after its ninth trip through the loop in the specific example being described. This may be accomplished by a gate connected to the a arm of hybrid junction 21 which is normally open but which is closed when gated ampliiierr 26 is open. However, as shown in Fig. 2, the amplifier 23 will also serve the purpose even though the maximum number of useful trips will be decreased by one. The timing of the control pulses of wave form V which control the gating of amplifier 23 is determined mainly by the numaes-spo? 'her off: trips thata pulse is; required .to `make and Ntheloop delay. .In1the instant embodiment, the gate isfheldopenffor .6 of 'a'period to Vpermit the sixpulseslnormally `circulatingto pass and then --closed for .4 of a period'to block anyunwanted pulses. If the pulses were to make eight useful trips throughthe loop, .the pulses-of'wave form V would be positive for .8 of a period'and negative for '.2 which would reduce the unused portion ofthe cycle.

#If fthe pulse :period is extremely short, th 'jnumber of trips through theloop may be decreased if desired by inserting additional .ex- Apanders in the repeater.

It will be noted that the incoming pulses are not only reshaped but are also accurately reftimed; Even though the time separation .of ad- Vjacent incoming pulses may vary from pulse to pulse, the'frequency of the output of thetiming circuit comprising fthe rectifier I3 pulse rate filter Hl` andpulse generator I6 will change lonly in response to the slow variations in the pulse repetition rate so that-those pulsesl whose peaks ihave been shifted slightly from their nominal Voccurrence time will be returned to their properl occurrence time relative to the other pulses as is Yshownbythe'wave forms of Fig. 3. Also, the "timing-v circuit is designed to have suiiicient fly- -Wheel effect lso that the control pulse trains will "be unbroken even through there are no lpulses for several periods.

YIt vmaybe desired to separate the gating func- "tion from the input andl output amplifiers I1 and `26if,`for example, suiiiciently wideband control ofthe traveling-'wave tube electron current carinot be obtained with thefgrid-cathode Vstructure or Where better gainsand stabilities canbe obvtained by separating the two functions. The traveling-wave ampliiiers I1 and 26 would there- "'fore'be'4 biased in the manner normal Yfor amplification'andV additional gates could be connected before the'respective amplifiers. For example, hybrid gates such as shown in Fig. 6 could be used. These gates are As tructurally similar to the lexpander 2 1 andlimiter 22. The crystal rectiiiers 6| are Vmatchedito their associated wave guide arms so that they normally present, to incidentenergman impedance equal to the characteristic impedance of the guide and hence absorb most of theinput power. When the gatey a high degree of mismatch s'o that all of the in- Y put power will be reilected in proper phase into the output arm of the hybrid junction.

Since the structure of the blanking gate shown in Fig. 6 is similar to that of the expander and limiter, either of the latter may be connected to perform the blanking function as well as their normal function. l

Although the invention has been described with particular reference to a specific embodiment, numerous other modifications Will readily occur to one skilled in the art without deviating from the spirit or scope of the invention. Further, the invention is not limited in its application to pulse repeaters; for example, it may be applied to terminal, testing, or other radio equipment wherein it is desired to periodically sample a signal wave and to alternatively increase or attenuate the amplitude of the sample.

4'whichY comprises-means for gating a narrowcas- `'ment-in time :of each ofzsaid pulses at: the-midperiod of' the vnominal pulse'foccurrence times,v ja circulating pulse y regenerator'comprising an .ex-

'panden a limiter, apu1seamplifieranda delay circuit connected in Ja .loop circuit, means for vinjecting said narrow Vsegments into said vcir- --culating pulse regenerator,.,means connected to said loop circuit for gating-said sections out oi. said circulating pulse regcnerator after apredetermined 'number of 'traversals through said loop, and means in said loopcircuit to remove the portion of anypulse Which remains in said vciic1`1latingpulse regeneratorfafter the nominal time for its removal from said tregenerator.

2. A pulse shaping circuit `for periodic pulses 'A which comprises la circulating pulse regenerator comprising V'an expander, a limiter, and a pulse amplifier connected in a loop circuit, means to gate a narrowsection in time of each of said pulses at the mid-period -of its nominal occurrence time 'into said pulse regenerator, means to gatesaid section out of lsaid pulse regenerator input Vgate connected to said'V loop circuit, means `to applyjsaid Ypulses to said input gate, asecond circuit connected to -receive vsaidfpulses which derives fromrtheincomingsignala iirst control ,wave comprising control pulses lwhich occur at themid-period of the nominal Isignal pulse oc- Vourrencej-tirne, said-control pulse being narrow relative toh said signal pulses,` means to apply said iirst Acontrol wave to saidI inputgate to open it during the Voccurrence, of said controlpulses,

an output gate connected to said loop circuit, means comprisingsaid*second-circuit to derive a secondv control wave comprising control pulses Awhich occur at 'the predetermined and unique 'time thatthe :pulses circulating in said loop shall appear at'the input tosaid output gatefaftera predetermined number of traversals through Asaid loop, means Jto apply `said secondicontrolVV wave .to said output gate toropen it during the oc-' currence of ,thel control' pulses which Acomprise,

pulses which comprise the said third control wave.

4. A pulseshaping circuit for periodic pulses which comprises means for gating said pulses to obtain narrow segments therefrom, a loop circuit comprisingl an expander, a limiter, and a pulse ampliiier, means for injecting said segments into said loop circuit and means for abstracting said segments from said loopcircuit at a later time.

5. A pulse-shaping circuit for periodic pulses of an originally standard amplitude which come prises an input circuit forgating said pulses to obtain narrow segments therefrom, .an expander adapted to increase the amplitude of all segments of greater vthan a predetermined portion relative to all other segments, apulse amplifier,

a limiter adapted to set a maximum amplitude for said segments, circuit means to recurrently circulate said segments through said expander, said amplifier and said limiter, an output circuit, and

means for gating said segments into said output circuit after a predetermined number of traversals through said expander and amplifier.

6. The combination in accordance with claim wherein said circuit means comprises a delay circuit proportional to circulate said segments through said expander and amplifier for their said predetermined number of traversals without overlapping.

V7. A pulse-shaping circuitfor periodic pulses of an originally standard amplitude which comprises an input circuit to receive the signal Wave bearing said pulses, a timing circuit connected to said input circuit for deriving a plurality of control Waves comprising trains of recurrent pulses of predetermined occurrence times relaf tive to said periodic pulses, means under control oi' a iirst of said pulse trains for gating a narrow segment of said signal Wave at the mid-period of each nominal pulse occurrence time, a circulating pulse regenerator, means for injecting said segments into said regeneraton said Vregenerator comprisingV means for increasing the amplitude Vof all segments greater than a predetermined portion of said standard amplitude relative to all others, means to limit the maximum amplitude of said segments, and means to amplify said segments connected in a loop circuit, an output circuit, and means under control of a second of said pulse trains for gating each of said segments into said output circuit after a predetermined number of traversals through said loop.

V8. The combination according to claim 7 and means in said loop circuit under control of a third of said pulse trains for blanking any portion of said segments which should remain in said loop circuit after their predetermined number of traversals through said loop.

9. A pulse regeneration circuit for recurrent pulses which comprises means to gate said pulses to obtain short segments representative of the instantaneous amplitude of said pulses at their nominaloccurrencetime, a loop circuit contain-V Hments into said loop circuit, means to abstract said segmentsA from said loop after a predetermined number Yof Vtravers'als through 'said loop, and means for disabling said ar'npliiierV during the VVmeans to derive a voltage having a frequency equal to the average repetition rate of input pulses, means to apply said recurrent pulses to said timing circuit,v means to derive from said voltage a iirst train of control pulses narrow relative to said recurrent pulses and synchronized with the mid-period oi the nominal pulse occurrence times, means under control of said first train of pulses to gate said recurrent pulses to obtain narrow segments therefrom, means to apply said segments to said input, means comprising said voltage to derive a second train of control'pulses of substantially the same Width as the pulses of said iirst train and synchronized with the occurrence at said output of segments which have completed a predetermined number of traversals through said loop, and means under control of said second train of pulses to abstract said segments from said loop.

11. The combination-in accordance with claim 10 and a delay circuit in said loop circuit adjust- -ed to return said segments during their prede- ROBERT L. CARBREY. Y

CAssrUs C. CUTLER. CARL B. H. FELDMAN.

References Cited in the iile of this patent UNITED STATES PATENTS Number I Name A Date 2,429,227 Herbst Oct. 21, 1947 2,468,058 Grieg Apr. 26, 1949 2,482,973

Gordon Sept. 27, 1949 

